BH6505K Datasheet, PDF (10/12 Pages) Rohm – PWM driver for CD and MD players

Optical disc ICs
BH6505K
FCircuit operation
(1) PWM driver
This is an H bridge driver with four N-type FETs in the out-
put stage. Output polarity and PWM duty vary in propor-
tion to the input differential voltage between VC, and to
the absolute value. The load is direct-PWM-driven by the
square wave with this varying duty.
This is a voltage feedback driver and so delivers a
constant gain regardless of battery voltage variation.
(2) DC / DC converter
The DC / DC converter that generates the voltage need-
ed to drive the FETs of the output-stage H bridge. Pre.VCC
is raised to 6.5V by attaching an inductance, Schottky
barrier diode, and capacitor.
(3) Triangular wave generator
(1) Freerunning
The free-running oscillation frequency of the triangular
waves can be set with an attached resistor (Rt, between
pin 16 and the ground) and capacitor (Ct, between pin 15
and the ground). The triangular wave has an amplitude
of 3 / 5 Pre.VCC at the top and VF (approximately 0.7V)
at the bottom. The ratio between rise time and fall time
is 3 : 1. Free-running frequency (ft) is determined with the
following equation:
3
1
ft= ₄ S
Ct S Rt 1*
VF
3
5
Pre.VCC
(2) Clock synchronization
The triangular wave can be synchronized by inputting to
the CLK pin (17 pin) a pulse wave equal to 0–Pre.VCC
(Vp-p). The following precautions should be kept in mind:
S The amplitude of the triangular wave decreases as the
clock frequency rises.
S The PWM driver is a voltage feedback driver, which
should preclude any problems unless the setting is such
that the triangular wave has an extremely small ampli-
tude.
S As mentioned above, a capacitor and resistor are also
required during clock synchronization.
FOperation notes
Attach a bypass capacitor (roughly 1µF) to the power
supply, at the base of the IC.
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